The subsidizing macrotidal transgressive barrier estuarine system of the Eastern Amazon coast, Northern Brazil

SOUZA FILHO, PEDRO WALFIR; LESSA. G. C.; COHEN, MARCELO; COSTA, F.R.; LARA, RUBÉN JOSÉ

Geology of Brazilian Coastal Barriers

Springer-Verlag

Lugar: New York; Año: 2008; p. 1 - 29

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 90.0pt 72.0pt 90.0pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The northern Brazilian coast, east of the Amazon River, is characterized by several large macrotidal barrier-estuarine systems that harbor the largest mangrove area in the world, with approximately 7,600 km2. One of these systems is the Caeté transgressive barrier estuarine system that has been the site of intensive investigations since 1995 and is considered as a proxy for the regional coastal morphostratigraphy. Data derived from surface sediment samples, vibra- and percussion-cores, radiocarbon dating, and pollen analysis, allowed for a detailed stratigraphic interpretation of a 25 km long profile across the system and the reconstruction of paleo-environmental changes in the mangrove plain. On the basis of lithology, sedimentary structures, texture, color, elevation and bounding surfaces, ten sedimentary facies were identified. Coastal evolution during the last 5,100 14C yr B.P. has been apparently modulated by small scale subsidence events, with the onset of three phases of barrier development. Mud deposition has apparently occurred behind the two landward most barriers between 5,913 cal yr BP to 3,736 14C yr BP. After 2,100 14C yr B.P., with the development of the last barrier island, about 20 km of mud deposition and mangrove progradation occurred inside the estuary. Contrary to the generally accepted idea that macrotidal settings (tidal range > 4 m) are not conducive to barrier formation, estuaries in this macrotidal coast are barred by sand bars in a truly transgressive fashion.